1. Field of the Invention
The present invention relates to an apparatus and a method for coding and/or decoding image data of moving pictures.
2. Description of Related Art
Various techniques for reproducing JPEG 2000 images are proposed. JP 2004-129217A discloses a technique of variable speed playback of JPEG 2000 images capable of performing normal speed playback or slow speed playback for each frame. In this publication, when three-level subband decomposition is performed, for example, image codes of only the decomposition levels 2 and 3 are decoded during the slow playback, while image codes of all the decomposition levels are decoded in order to include higher frequency components (higher resolution components) during the normal speed playback.
Another publication, JP 2003-338995A, discloses a technique of high-speed playback of JPEG 2000 images coded on a frame basis. In this publication, code streams are decoded across the frequency components (from the lower frequency components to higher frequency components) in certain frames at prescribed frame intervals, while code streams of only lower frequency components are decoded in the rest of the frames. As the playback speed increases, the frame interval of the certain frames is increased.
Currently, Motion-JPEG 2000 performing frame-by-frame hierarchical coding is spreading. It is pointed out, however, that a problem arises with this moving picture coding scheme in conjunction with real-time decoding due to the JPEG 2000 algorithm being complicated. To overcome this problem, code streams of only the lower-frequency (lower-resolution) components are decoded in order to compensate for insufficient processing capability. The proposals of the above-described two publications are also made from the same viewpoint.
However, these conventional techniques do not make full use of the characteristics and features of the JPEG 2000 coding scheme. In spite of the fact that JPEG 2000 images consist of a set of codes having various attributes, including resolution levels, positions, color components and image qualities, the conventional techniques focus attention only on the resolution level.